docs: def formatted_prefix(self, **format_info):
          """
          Gets a dict with format info, and formats a prefix template with that info. For example:
          if our prefix template is:
          'some_file_{groups[0]}_{file_number}'
  
          And we have this method called with:
  
          formatted_prefix(groups=[US], file_number=0)
  
          The returned formatted prefix would be:
          'some_file_US_0'
          """
          prefix_name = self.prefix_template.format(**format_info)
          file_number = format_info.pop('file_number', 0)
          if prefix_name == self.prefix_template:
              prefix_name += '{:04d}'.format(file_number)
          for key, value in format_info.iteritems():
              if value and not self._has_key_info(key):
                  prefix_name = '{}-{}'.format(prefix_name, ''.join(value))
          return prefix_name